Implantable System for Long- and Short-Term Active Charge Balancing in Neural Electrical Stimulation

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Functional electrical stimulation is a technique that allows for the stimulation of nerves by electrical charge. In order to avoid charge accumulation which causes tissue lesion and electrode corrosion, in particular during long-term treatments, charge balancing has become an integral part of functional electrical stimulation. However, for reliability reasons, most CE-certified medical devices are equipped with passive charge balancing systems today, despite their large size, long settling time, and uncontrolled charge compensation. A promising approach to small, fast, and well controlled charge compensation is active charge balancing. This technique also comes up with the advantage of a better signal quality when measurements and stimulations are performed simultaneously. In this project, fundamental research will be performed on electrical stimulation using active charge balancing in order to reduce the risks of stimulation and facilitate save chronic trials. The objective is to develop and evaluate a CMOS integrated, high-voltage compatible charge balancing system, which can be used in combination with a variety of stimulators. In addition to the typical requirements on implantable systems, e.g., low-power consumption and low-area demand, the diversity of common applications necessitates a high adaptability and flexibility of the active charge balancing system in terms of, e.g., configurable safety limits, output current limitation and adaptive supply rails with high-voltage compatibility up to 30V.In order to meet these requirements and to achieve a well-defined charge balancing, the complementary approaches to active charge balancing for long- and short-term stimulation will be considered and pursued, both separately and in combination. Each approach represents a sufficiently well performing control loop while providing the opportunity to achieve a better performance in charge balancing when being combined with each other. Considering multiple-electrode configurations and thus multiple-input multiple-output systems, approaches to linked control loops will be considered and developed and their stability, interaction, and performance evaluated.